Hello Topbanders,
For the past few months I have been plagued by what I suspected was power
line noise on 160 meters, and finally was able to track it down to a power
line pole 0.66 miles from my house and learned a bunch during the process.
While this topic has been covered in the past, I thought some info from my
recent exercise might be useful to others (and a good reminder of what
techniques work). Here is a link to a simple website I created that
contains pictures, oscilloscope screen shots of receiver audio, and links
to video recordings that I made.
http://sites.google.com/site/powerlinenoise/
The factors which really helped locate the noise source were as follows :
1) My 160 meter pennant RX antennas indicated the noise was originating NE
from my house.
2) Ability to hear the noise on 1710 khz on my car radio while driving
around which helped me zero in on a section of power lines (but it was
impossible to zero in on a particular pole).
3) Observing (using oscilloscope screen shot of audio on 160 meters using
radio in AM mode) that noise frequency was 120 hertz which is typical of
power line equipment arcing (arcing each half of the sine wave).
4) Direction finding using VHF AM radio (portable scanner with AM aircraft
band capabilities listening on 136 MHZ) using a portable 4 element
horizontal beam and 20 dB attenuator that I was able to switch in as I got
close to the source.
Notes :
1) I tried using a portable 160 meter AM radio with portable shielded DF
loop, but I was unable to zero in on the suspect pole (with 100 percent
certainty) using this equipment, and it was not until I used the VHF AM
radio with lots of attenuation that I was able to identify the suspect pole.
2) VHF direction finding beam worked much better when mounted horizontally
(peak and null data made much more sense).
3) I used EZNEC demo to confirm the amount that I need to lengthen the
elements on my two meter beam in order to maintain the proper beam pattern
when used on 136 MHZ. I used alligator clips to lengthen the elements and
this worked out just great (nothing fancy).
73's
Don (wd8dsb)
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Stew Perry Topband Distance Challenge coming on December 29th.
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